System and method for unscheduled wireless communication with a medical device

ABSTRACT

Data is communicated from a transmitter of an external unit to a receiver of an implantable medical device. The receiver of the implantable medical device operates in a wide band receiver mode to detect the transmission from the external unit and operates in a narrow band receiver mode to receive the data.

CROSS-REFERENCE TO RELATED APPLICATIONS

Cross-reference is made to commonly assigned related U.S. Applicationsfiled on even date: Ser. No. 11/224,593, entitled “SYSTEM AND METHOD FORUNSCHEDULED WIRELESS COMMUNICATION WITH A MEDICAL DEVICE” by Gregory J.Haubrich; Len D. Twetan; David Peichel; Charles H. Dudding; George C.Rosar; and Quentin S. Denzene Ser. No. 11/224,595, entitled“COMMUNICATION SYSTEM AND METHOD WITH PREAMBLE ENCODING FOR ANIMPLANTABLE DEVICE” by Gregory J. Haubrich, Javaid Masoud, George C.Rosar, Glenn Spital, and Quentin S. Denzene; and Ser. No. 11/224,594,entitled “IMPLANTABLE MEDICAL DEVICE COMMUNICATION SYSTEM WITH MACRO ANDMICRO SAMPLING INTERVALS” by Glenn Spital.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to implantable medical devices. Morespecifically, the present invention relates to implantable medicaldevices with communication systems.

2. Description of the Related Art

Implantable medical devices (IMDs) are now used to provide countlesstherapies and to monitor a wide variety of physiological events.Conventionally, communication with IMDs has been with inductive couplingcommunication systems. Such systems, however, are generally only capableof communicating over very short distances. As a result, a magnetic headof a programmer (or other external device) must be located very near theIMD for communication to occur. More recently, radio frequency (RF)communication systems have been developed for use with IMDs. RFcommunication provides a number of benefits over inductive couplingcommunication systems, including much greater communication distances.

Because an IMD is implanted within the body of a patient, battery usageis one consideration for an IMD communication system. Methods ofreducing the amount of time that the receiver of an IMD operates can bebeneficial in improving power consumption.

BRIEF SUMMARY OF THE INVENTION

Data is communicated in a transmission between an external unit and animplantable medical device having a receiver that operates in a wideband receiver mode and a narrow band receiver mode. In the wide bandreceiver mode, the receiver detects a transmission on any one ofmultiple communication channels. In the narrow band receiver mode, thereceiver receives the data from one communication channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a communication system forcommunicating data between an implantable medical device (IMD) and anexternal unit.

FIG. 2 is a block diagram illustrating the components of the IMD and theexternal unit that make up the communication system.

FIG. 3 is a graphical illustration of a transmission bit streamincluding an encoded preamble and data.

FIG. 4 is a graphical illustration of pulse width encoding.

FIG. 5 is a graphical illustration of channel data embedded in thepreamble with pulse width encoding.

FIG. 6 is a table illustrating frequency shift encoding.

FIG. 7 is a graphical illustration of communication mode data embeddedin the preamble with frequency shift encoding.

FIG. 8 is a block diagram of a receiver of the IMD.

FIG. 9 is a flow chart illustrating a method of operating the receiver.

FIG. 10 is a timing diagram illustrating an alternate method ofoperating the receiver.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram illustrating communication system 10 thatenables communication between IMD 12, and external unit 18. In oneembodiment, IMD 12 is an implantable cardioverter defibrillator (ICD),but the present invention is equally applicable to many types of medicaldevices, including both implantable medical devices and external medicaldevices. IMD 12 is capable of providing therapies and/or sensingphysiological events of the heart of patient P via lead 14. Antenna 16is used to communicate with external unit 18 and may be any devicecapable of sending or receiving electromagnetic energy, including, forexample, a surface mounted antenna, an inductor, or a half-wave strip.

External unit 18 is a device, such as a medical device programmer,capable of communication with IMD 12 via antenna 20. External unit 18includes antenna 20, which may be any type of RF antenna capable ofcommunicating in the desired RF frequencies with IMD 12, and may belocated inside or outside of a housing of external unit 18.

FIG. 2 is a block diagram illustrating some of the components of IMD 12and external unit 18 that make up communication system 10. External unit18 includes antenna 20, external unit circuitry 27, and transceiver 28.Antenna 20 is coupled to transceiver 28 of external unit 18. Externalunit circuitry 27 includes a microcomputer and software to control theoperation of external unit 18. Transceiver 28 enables external unitcircuitry 27 to transmit and receive communications with IMD 12.Transceiver 28 of external unit 18 includes transmitter 32 and receiver34.

IMD circuitry 29 includes a microprocessor for controlling the operationof IMD 12 and for processing data, therapy delivery circuitry fordelivering a therapy through lead 14, and sensors for generating data,including data generated by detecting electrical signals on lead 14.Transceiver 30, coupled to antenna 16, enables IMD circuitry 29 totransmit and receive communications with external unit 18. Transceiver30 includes transmitter 36 and receiver 38, which transmit and receivedata using RF electromagnetic waves.

Communication between IMD 12 and external unit 18 can be performed overany communication band. In one embodiment, the communication occurs overa public radio frequency band. In another embodiment, the communicationoccurs over the Medical Implant Communication (MICs) band between 402MHz and 405 MHz. Although the present invention is described withreference to radio frequency bands, it is recognized that the presentinvention is also useful with other types of electromagneticcommunication.

Because IMD 12 has a finite battery capacity, one consideration in thedesign of RF communication system 10 is the energy efficiency of IMD 12.One factor in the energy efficiency of IMD 12 is the time transceiver 30is engaged in actively transmitting or receiving. Thus, an improvementin energy efficiency of transceiver 30 will lead to increased batterylife of IMD 12. Energy efficiency is less of an issue in the design ofexternal unit 18, because external unit 18 is generally connected to anexternal power source such as a 120V AC. Therefore, reducing the energyconsumption of transceiver 30, even in exchange for additional energyconsumption of transceiver 28, is beneficial.

While transmitters only need to be turned on when there is something totransmit, receivers are turned on much more frequently. No communicationcan take place unless the receiver is on, at least momentarily, todetect an attempted transmission. To provide a fast response time, areceiver may sample a communication channel as often as twice everysecond or more; but, a receiver that turns on just twice every secondwill turn on 172,800 times in one day. A transmitter, on the other hand,may turn on only a handful of times in that same period. Therefore, anincrease in the energy efficiency of a receiver can provide an increasein the effective life of the power supply.

Returning to communication system 10 of FIG. 2, transmitter 32 transmitsa preamble signal prior to the transmission of data. Receiver 38 samplesthe communication channels periodically for this preamble signal, ratherthan remaining on at all times, while still ensuring that receiver 38will not miss the transmission of any data. The preamble signal containsa modulation pattern recognizable by receiver 38. If receiver 38 detectssignals on a communication band, but finds that the signals do notcontain the modulation pattern, receiver 38 can shut down since thedetected signal is not a communication initiated by transmitter 32 forreceiver 38. Furthermore, the preamble signal contains embedded datathat allows the receiver 38 to further improve efficiency. This dataprovides link-pertinent information (such as receiver channel andcommunication mode) for the subsequent transmission of data. Receiver 38may continue operating in a low power receiver mode while receiving theembedded data, and then adjust its receiver configuration settings asspecified by the embedded data to initiate the higher power receivermode for receipt of the transmitted data.

Receiver 38 of IMD 12 (described in more detail below with reference toFIGS. 8-9) operates in a low-power, wide band receiver mode that cansimultaneously sample for energy on multiple communication channels, anda narrow band receiver mode for communication on a single channel.

FIG. 3 is a graphical illustration of a transmission bit stream 40transmitted by transmitter 32. Transmission bit stream 40 includespreamble signal 42 and data 48. In one embodiment, preamble signal 42has a duration greater than or equal to a fixed duration, referred to asthe macro sampling interval. By transmitting preamble signal 42 forgreater duration than the macro sampling interval, receiver 38 canperiodically sample received energy for a communication, but turn offbetween samples. The off-time of receiver 38 conserves energy ascompared to having receiver 38 on continuously.

Preamble signal 42 includes wake up segment 44 and ready segment 46. Toensure its detected by receiver 38, wake up segment 44 is the segmentthat first informs receiver 38 that transmitter 32 is attempting tocommunicate. Wake up segment 44 is transmitted for a duration greaterthan the macro sampling interval of receiver 38. Wake up segment 44includes sync pattern 50 that informs receiver 38 that data 48 is aboutto be transmitted and embedded channel data 52 that informs receiver 38on which channel that data is to be transmitted.

Sync pattern 50 is a repeating pattern of bits. In one embodiment, syncpattern 50 is a transmission of alternating on-off keyed (OOK) 0 and 1bits, each bit having a duration of about 50 microseconds to create aseries of repetitive pulses having about 50 microsecond on-time andabout 50 microsecond off-time. This transmission results in atransmitted tone having a frequency of about 10 kHz. One of the benefitsof OOK sync pattern 50 is that receiver 38 can be designed with a verysimple, low-powered OOK or AM receiver capable of detecting thetransmission and validating the modulation of the transmission. Ifenergy is detected that does not contain this modulation pattern,receiver 38 can quickly identify the energy as something other than thedesired transmission and shut down to conserve energy. Sync pattern mayinclude any recognizable pattern of bits, at any desired bit frequency.Other types of modulation could also be used to validate the modulationpattern, such as amplitude modulation (AM) or vestigial sidebandmodulation (VSB), phase shift keying (PSK), frequency shift keying(FSK), etc.

During transmission of wake up segment 44, transmitter 32 alternatesbetween transmission of sync pattern 50 and channel data 52. However,channel data 52 is encoded within sync pattern 50 in such a way that thedetection and validation components of receiver 38 do not notice theembedded data. In one embodiment, receiver 38 includes a transitiondetector that detects the leading edges of sync pattern 50, and channeldata 52 is embedded in such a way that the leading edges continue in thesame pattern as sync pattern 50, but the falling edges are adjusted toencode data. In other words, the pulse width of sync pattern 50 ismodified to embed channel data 52 within wake up segment 44. Channeldata 52 is described in more detail with reference to FIGS. 4-5 below.

Following wake up segment 44, transmitter 32 transmits ready segment 46that informs receiver 38 that transmission of data 48 is about to takeplace and also provides additional encoded configuration data. Readysegment 46 includes sync pattern 50 and mode data 54. In one embodiment,sync pattern 50 of ready segment 46 is phase shifted 180 degrees fromsync pattern 50 of wake up segment 44, such that receiver 38 candifferentiate between wake up segment 44 and ready segment 46. In analternate embodiment, receiver 38 differentiates between wake up segment44 and ready segment 46 by detecting encoded mode data 54 within readysegment 46. Sync pattern 50 of ready segment 46 can be any otherdistinct pattern of bits which can be distinguished from sync 50 of wakeup segment 44.

Ready segment 46 is transmitted for a period of time greater than amicro sampling interval of receiver 38. After receiver 38 has detectedand validated wake up segment 44, and decoded channel data 52, receiver38 resumes sampling, but now at a shorter interval, referred to as themicro sampling interval. Because ready segment 46 has a greater durationthan the micro sampling interval, receiver 38 will detect ready segment46 prior to the transmission of data 48 from transmitter 32, while stillconserving power until detection of ready segment 46.

Embedded within ready segment 46 is encoded mode data 54, which providesreceiver operating mode data to receiver 38. This data may include linkpertinent information such as desired data rate and/or telemetryprotocol for the transmission and reception of data 48. In oneembodiment, mode data 54 is embedded within ready segment 46 usingfrequency shift encoding. Similar to phase shift encoding describedabove, frequency shift encoding maintains the OOK packet structure ofsync pattern 50 to enable receiver 38 to continue detecting andvalidating the modulation pattern of preamble 42. However, rather thanadjusting the pulse width of sync 50, frequency shift encoding adjuststhe transmission frequency slightly to encode mode data 54. Frequencyshift encoding is further described with reference to FIGS. 6-7.

After transmitter 32 has completed the transmission of preamble 42, data48 is transmitted. Data 48 may include pure data, messages, requests fora response, and/or any other desired communication between transmitter32 and receiver 38. All types of data 48 are referred to generally asdata.

FIG. 4 is a graphical illustration of one embodiment of a pulse widthencoding scheme to encode data within wake up segment 44. Pulse widthcodes include sync pattern 50, zero pattern 56, and one pattern 58. Syncpattern 50, as previously described, is a repeating pattern of OOK 0 and1 bits. Each box of FIG. 4 represents one half of a bit length, where ashaded box represents a transmission and an unshaded box represents notransmission. In one embodiment, each bit of sync pattern 50 is 50microseconds long, such that each box of FIG. 4 represents 25microseconds.

Pulse width encoding enables data to be encoded within wake up segment44 without affecting the timing of the leading edges of the bits of thetransmission and also maintaining an overall 50% duty cycle. Maintaininga consistent timing of the leading edges allows receiver 38 to verifythat the transmitted signal conforms to the appropriate modulation. Byadjusting only the trailing edge of the bits, the leading edges remainunchanged.

Zero pattern 56 includes two pulses. Each of the pulses has a leadingedge that is equivalent to the leading edge of sync pattern 50. Thefirst pulse has a duration of one-half of a sync bits, and the secondpulse has a duration of one and a half of a sync bit. Although the widthof the pulses have been varied, the overall duty cycle of zero pattern56 remains 50%.

One pattern 58 also includes two pulses, with each pulse having aleading edge that is equivalent to the leading edge of sync pattern 50.The first pulse has a duration of one and a half of a sync bit, and thesecond pulse has a duration of one-half of a sync bit. One pattern 58also has an overall duty cycle of 50%.

FIG. 5 is a graphical illustration of channel data encoded with pulsewidth encoding on a portion of wake up segment 44. The portion of wakeup segment 44 shown includes sync pattern 50 (repeated once), five bitsof encoded channel data 52, followed by another sync pattern 50(repeated once). Periodically between transmissions of sync pattern 50,channel data 52 is transmitted.

Channel data 52 allows receiver 38 to sample all channels of acommunication band at once with a low power wide band receiver. Onceenergy has been detected, receiver 38 decodes the communication channelfrom channel data 52 and adjusts receiver 38 to the appropriate channel.In this way, receiver 38 is able to conserve energy by determining theappropriate communication channel without having to scan each channelindividually.

In the embodiment illustrated in FIG. 5, channel data 52 is binary datahaving five bits. FIG. 5 also shows pulse width encoded channel data ofthe binary code for channel 1 (00001) transmitted between sync patterns50. Additional link pertinent information (e.g. data rate, channel,device ID, etc.) could also be transmitted to receiver 38 using the samepulse width encoding technique, if desired. Channel data 52 is repeatedperiodically within wake up segment 44.

After receiver 38 has received channel data 52 and has adjusted to theappropriate communication channel, it next monitors for ready segment 46containing mode data 54. Ready segment 46, consists of sync pattern 50and encoded mode data 54. As described above, in one embodiment, syncpattern 50 of ready segment 46 is shifted 180 degrees from sync, pattern50 of wake up segment 44.

FIG. 6 is a table illustrating frequency shift encoding of ready segment46. With receiver 38 adjusted to receive the appropriate communicationchannel, mode data 54 is communicated to receiver 38 through frequencyshift encoding of sync pattern 50. Sync pattern 50, is transmitted atcenter frequency (fo) of the communication channel. By adjusting thisfrequency up or down, data can be encoded on ready segment 46, whilestill maintaining the (phase shifted) leading edges and modulation ofsync pattern 50. In one embodiment, data is encoded by shifting syncpattern 50 up or down 100 kHz from center frequency (fo). To transmit abinary zero bit, sync pattern 50 is shifted down 100 kHz from centerfrequency (fo). This frequency is referred to as low frequency (fL), andis represented graphically by a downward pointing arrow. To transmit abinary one bit, sync pattern 50 is shifted up 100 kHz from centerfrequency (fo). This frequency is referred to as high frequency (fH),and is represented graphically by an upward pointing arrow.

FIG. 7 is a graphical illustration of a portion of ready segment 46including frequency shift encoded mode data 54. This portion of readysegment 46 begins with phase shifted sync pattern 50. After sync pattern50, mode data 54 is encoded within ready segment 46 by shifting thepattern of sync pattern 50 up or down in frequency. Any binary data ofany length can be encoded within ready segment 46 using this frequencyshift encoding technique. Mode data 54 can be transmitted once orrepeated periodically within ready segment 46. In one embodiment, modedata 54 instructs receiver 38 of the appropriate telemetry protocol touse in receiving of data 48 from transmitter 32.

Now that transmitter 32 and transmission bit stream 40 have beendescribed, the design and operation of receiver 38 of IMD 12 will bedescribed.

FIG. 8 is a block diagram of one embodiment of receiver 38 of IMD 12capable of receiving and processing preamble signal 42. Receiver 38includes OOK (or AM) receiver 70, voltage controlled oscillator (VCO)72, adjustable filter 74, threshold detector 76, digital to analogconverter (DAC) 78, transition detector 80, phase locked loop (PLL) 82,RC oscillator 84, timer 86, and control circuitry 88.

OOK receiver 70 is a wide band receiver capable of receiving more thanone channel at a time, such as a super regenerative receiver, whichrequires very low power consumption but provides very high sensitivity.One example of a super regenerative receiver is described in U.S. Pat.No. 4,786,903 by Grindahl et al.

In one embodiment, OOK receiver 70 is an adjustable receiver capable ofbeing adjusted between a wide band mode capable of simultaneouslyreceiving signals on all channels of a communication band and a narrowband mode capable of receiving signals on only a single channel of thecommunication band. In another embodiment, OOK receiver 70 is a wideband receiver that is operated in parallel with a narrow band receiversuch that either or both receivers can be operated at any one time.Receiver 70 can also be another type of receiver, such as an amplitudemodulation (AM) receiver. VCO 72 supplies a reference frequency to OOKreceiver 70 to tune it to the appropriate receiver frequency.

Following OOK receiver 70 is adjustable filter 74, which is anadjustable low-pass filter used to filter out signals having undesiredfrequencies. Threshold detector 76, following adjustable filter 74,determines whether the amplitude of the received signal exceeds athreshold amplitude. A reference threshold amplitude is fed intothreshold detector by DAC 78. Transition detector 80 follows thresholddetector 76 and detects the leading edges of a received signal.Connected to transition detector 80 is PLL tone decoder or correlator82, which determines how well an input signal correlates with anexpected signal and generates a signal to adjust VCO 72 as needed.

RC oscillator 84 provides the time base for receiver 38. RC Oscillator84 and timer 86 work in conjunction to provide appropriate timingsignals to logic and state machines within control circuitry 88. Controlcircuitry 88, which controls the operation of receiver 38, may alsoinclude a microprocessor. Control circuitry 88 controls VCO 72, OOKreceiver 70, adjustable filter 74, and DAC 78, and receives inputs fromvarious components to enable it to monitor and control the operation ofreceiver 38. Control circuitry 88 also interfaces with IMD circuitry 29of IMD 12.

FIG. 9 is a flow chart illustrating a method of operating receiver 38,begins by sampling the communication band at each macro samplinginterval to detect whether the energy present within the communicationband exceeds a threshold amplitude (step 90). In this step, receiver 38operates in a wide band receiver mode to monitor all channels of thecommunication band at once. Receiver 38 turns on for only as long asneeded to determine whether any energy present on the communication bandexceeds the threshold amplitude. If no energy is present, receiver 38turns back off until its next sample at the macro sampling interval.

Once sufficient energy is detected in the communication band, receiver38 stays on verify whether the detected energy contains the modulationcharacteristic of preamble signal 42 of transmission bit stream 40 (step92). To do so, receiver 38 monitors the low-to-high transitions todetermine whether the transitions occur at the appropriate rate. Forexample, if wake up segment 42 is known to contain a 10 kHz bit pattern,receiver 38 monitors the energy to verify whether it corresponds to a 10kHz pattern. If it does not, then receiver 38 identifies the energy asnot being transmission bit stream 40 and turns off until its nextsample. If energy is detected that exceeds the threshold amplitude andcontains the appropriate modulation, receiver 38 then proceeds on theassumption that the energy present in the communication band istransmission bit stream 40.

After verifying modulation (step 92), receiver 38 remains on to monitorfor encoded channel information (step 94) within wake up segment 44. Asdescribed above, channel data 52 is encoded within wake up segment 44with pulse width encoding. Receiver 38 detects the pulse width encodingby monitoring for a series of uncorrelated bits (bits having a differentpulse width than sync pattern 50). The uncorrelated bits are identifiedas channel data 52 and decoded by receiver 38. Decoded channel data 52informs receiver 38 of the channel in which transmission bit stream 40is being broadcast by transmitter 32.

Knowing the appropriate channel, receiver 38 adjusts to thatcommunication channel (step 96). At the same time, receiver 38 isadjusted from the wide band receiver mode to a narrow band receiver modein which only the single channel identified by decoded channel data 52is received.

Following the adjustment to the appropriate channel, receiver 38continues to monitor the channel for ready segment 46 (step 98). Sincewake up segment 44 is longer than the macro sampling interval ofreceiver 38, transmission of wake up segment 44 will generally not becomplete by the time that receiver 38 has adjusted to the appropriatechannel. If no further data is needed from wake up segment 44, receiver38 has no need to continue receiving the rest of wake up segment 44.Accordingly, receiver 38 turns itself off for short periods of time butperiodically turns back on to sample wake up segment 44. The interval oftime between samples when looking for ready segment 46 is referred to asthe micro sampling interval, which is a period of time less than theduration of ready segment 46.

During each micro sample, receiver 38 determines whether wake up segment44 is still being transmitted or whether transmission of ready segment46 has begun (step 98). If wake up segment 44 is still beingtransmitted, receiver 38 turns off and resumes micro sampling untilreceiver 38 detects ready segment 46. Detection of ready segment 46 maybe, for example, by detecting a phase change or a frequency change.

Once ready segment 46 has been detected, receiver 38 stays on to monitorready segment 46 for encoded mode data 54. As described above, mode data54 is encoded with frequency shift encoding. Receiver 38 detects modedata 54 by monitoring for a frequency shift in sync pattern 50, eitherup or down from center frequency (fo). When mode data 54 is detected itis decoded by receiver 38 (step 100). Mode data 54 instructs receiver 38of the appropriate receiver mode for reception of data 48. Receiver 38then adjusts to the appropriate receiver mode identified by mode data 54(step 102). In one embodiment, the subsequent receiver modes (used toreceive data 48) consume more energy. By enabling receiver 38 to detectand evaluate initial communications, and to receive channel and modedata, all prior to entering the high power communication mode, valuableenergy savings are realized.

With receiver 38 now set to receive transmission bit stream 40 on theappropriate communication channel, and also configured to theappropriate receiver mode, transmitter 32 transmits data 48. Receiver 38receives data 48 (step 102) and determines whether any further action isrequired. If data 48 contains a request for further communication, forexample, receiver 38 passes that request to IMD circuitry 29 of IMD 12,which responds accordingly.

FIG. 10 is a timing diagram illustrating a second method of operatingreceiver 38, which includes operating in a wide band and a narrow bandreceiver mode. The diagram illustrates a repeating method of samplingfor a transmission on the communication band. Each cycle around thecircle represents a period of time, such as five seconds. Each cycleincludes ten time slots, represented by T1-T10, each spaced by a shortertime interval, such as 0.5 seconds. The method progresses around thecircle in a clockwise direction.

In a narrow band receiver mode, a transmission in the communication bandis detected by sampling each channel individually, checking for energypresent on that channel. Noise present in adjacent communicationchannels can be filtered out, resulting in improved receiversensitivity. This is useful when transmitter 32 is a long distance awayfrom receiver 38 (resulting in a very weak transmission signal) or in anoisy environment, and also for higher speed communication over anydistance.

However, sampling each channel individually results in a decreasedresponse time of the receiver and/or increased power consumption. Forexample, if the communication band includes ten individual channels, tensamples would be needed to check each channel for a communication.Furthermore, a communication present on one channel will only bedetected when receiver 38 is sampling that one channel, and not whenreceiver 38 is sampling any of the other nine channels.

In wide band receiver mode, detecting a transmission on one of thechannels of a communication band is achieved by simultaneously samplingthe entire band of ten channels with receiver 38. This method results inincreased receiver response time and reduced energy consumption. Becauseonly a single sample needs to be taken to detect a transmission, farfewer samples are required.

However, the wide band receiver mode is less sensitive than the narrowband receiver mode, because all noise in the communication band isreceived, including transmissions from other nearby devices and othernoise sources. As a result, the wide band receiver mode is best suitedfor slower speed communications over short distances.

Because there are benefits to operating in a wide band receiver mode,and other benefits to operating in a narrow band receiver mode, thisembodiment provides a method of operating receiver 38 in both receivermodes to sample for a transmission on a communication channel. Forexample, at T1, receiver 38 powers up in wide band receiver mode 110. Aspreviously described, wide band receiver mode 110 enables receiver 38 tosample all channels of the communication band at once. If energy isdetected, receiver 38 validates the signal and adjusts to the narrowband receiver mode to receive the communication, as described withreference to FIG. 9.

Since wide band receiver mode 110 is capable of detecting energy on anyof the channels, it is also less sensitive than the narrow band receivermode. If no energy is detected in wide band receiver mode 110, receiver38 adjusts to narrow band receiver mode 112, which provides improvednoise rejection and sensitivity over wide band receiver mode 110. At T1,narrow band receiver mode is centered on first communication channelCH1. Even though wide band receiver mode 110 did not detect energy onthe band, the increased sensitivity of narrow band receiver mode 112allows receiver 38 to detect a weaker transmission or to filter out thetransmission from a noisy environment. If energy is detected thatconforms to the appropriate modulation, receiver 38 receives thetransmission. If no energy is detected, receiver 38 turns off until thenext time interval at T2.

Receiver 38 repeats the process at T2 by first sampling in wide bandreceiver mode 110, and then in narrow band receiver mode 112. However,at T2 receiver 38 samples the second communication channel CH2, ratherthan the first communication channel. Receiver 38 continues in thismanner around the timing diagram until all channels have beenindividually sampled. If no energy is detected, receiver 38 repeats theprocess from T1 to T10. Receiver 38 performs a sample of allcommunication channels every 0.5 seconds, and performs a sample of eachindividual communication channel every 5 seconds.

This method enables receiver 38 to provide fast response times for closerange communications with wide band receiver mode 110, while alsoproviding high sensitivity for further distance communications or innoisy environments with narrow band receiver mode 112.

In another embodiment, receiver 38 includes a wide band receiver inparallel with a narrow band receiver. In this embodiment, receiver 38 iscapable of operating in both the wide band receiver mode and the narrowband receiver mode at the same time, thereby reducing the total on-timeof the receiver.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. In particular, one skilled in the art willrecognize that although the present invention has been described fortransmissions from an external device to an implantable medical device,it could also be implemented between implantable devices, betweenexternal units, among a wireless network of implantable and externaldevices, or for transmissions from implantable medical devices toexternal units. In addition, other known types of data encoding could beused to perform the same functions as pulse width encoding and frequencyshift encoding described above.

1. A medical device for receiving a transmission including data, themedical device comprising: device circuitry controlling operation of themedical device and processing data; and a receiver configured to operatein a wide band receiver mode that simultaneously monitors for atransmission on any of multiple communication channels and, in responseto detecting the transmission on one of the multiple communicationchannels, operate in a narrow band receiver mode that receives data onthe one of the multiple communication channels on which the transmissionis detected, wherein the receiver, in response to not detecting atransmission on any of the multiple communication channels in thewideband receiver mode, is configured to operate in the narrow bandreceiver mode on a first one of the multiple communication channels tomonitor for the transmission.
 2. The medical device of claim 1, whereinthe detected transmission further comprises embedded channel data, andthe receiver is configured to decode the embedded channel data in thewide band receiver mode and adjust from the wide band receiver mode tothe narrow band receiver mode at a channel identified by the channeldata.
 3. The medical device of claim 1, wherein the receiver isconfigured to turn off for a period of time when no transmission isdetected while monitoring for a transmission in the narrow band receivermode on the first one of the multiple communication channels.
 4. Themedical device of claim 3, wherein the receiver is configured to turnback on after the period of time, operate in a wide band receiver modethat simultaneously monitors for a transmission on any of multiplecommunication channels and, in response to not detecting a transmissionon any of the multiple communication channels, begin operating in thenarrow band receiver mode to monitor for a transmission on a second oneof the multiple communication channels.
 5. The medical device of claim1, wherein the medical device is an implantable medical device.
 6. Themedical device of claim 1, wherein the receiver, when operating in thewide band receiver mode, is configured to receive frequencies from 402MHz to 405 MHz.
 7. The medical device of claim 1, wherein the receivercomprises a super regenerative receiver configured to operate in thewide band receiver mode.
 8. The medical device of claim 1, wherein thereceiver is configured to detect the transmission on one of the multiplecommunication channels when an energy on any of the multiplecommunication channels exceeds a threshold energy and the detectedenergy contains an expected modulation pattern.
 9. The medical device ofclaim 1, wherein the receiver is configured to detect encoded mode dataindicating operating information for reception of the data.
 10. Themedical device of claim 1, wherein the transmission includes a preambleportion and a data portion, the preamble portion further including: awake up segment comprising a first sync pattern that informs thereceiver that data is following and embedded channel data that informsthe receiver on which channel the data is to be received, and a readysegment that includes a second sync pattern that differentiates theready segment from the wake up segment and encoded configuration datafor use in receiving the data, the receiver is configured to receive atleast a portion of the wake up segment while operating in the wide bandreceiver mode and receive the ready segment while operating in thenarrow band receiver mode.
 11. The device of claim 1, wherein thereceiver is configured to alternate between operating in the wide bandreceiver mode and operating in the narrow band receiver mode to detectthe transmission such that each time the receiver is operated in thenarrow band receiver mode the receiver samples a different one of themultiple communication channels for the transmission.